Various flange assembly structures are known for sealing tubular members for the flow of the fluid therein. Some of these have included an annular seal ring having a bifrustoconical shape, i.e. a radially inwardly tapered sealing surface extending from a central portion of the seal ring axially toward either end thereof. Typically, such a bifrustoconical seal ring is engaged in complemenarily sealing surfaces formed in a recess in ends of opposed tubular members. In U.S. Pat. No. 4,470,609, for example, the drawing of the tubular members toward each other cams a bifrustoconical saal ring to radially compress nonmetallic soft seals supported on the bifrustoconical surfaces to form a fluid seal between the tubular members and the seal ring. The use of such non-metallic soft seals is disadvantageous in some applications because such soft seals tend to be damaged more readily by the presence of dirt or foreign material, or are more readily adversely effected by elevated pressure and temperature of the fluid in the tubular members, and can extrude from the annular rings in which they are placed.
U.S. Pat. No. 3,507,506 also discloses a bifrustoconical seal ring which seats in annular recesses formed in adjacent mating flanges of tubular members. A peripheral groove is formed near the axial end of the seal ring to provide elastic, somewhat flexible noses, which are compressed against the shoulders of the annular recesses of the flanges to provide a primary sealing surface. Deformation of the noses in this manner provides a relatively small annular area for sealing which is more like a line-type seal than an area-type seal. In addition, a soft secondary seal is used in the frustoconical surfaces of the seal ring and is compressed against the annular sealing recess of the flange. Exposure of this seal to high temperature would result in an elasticity decrease of the seal ring, which in turn could lead to a compromised primary seal. The presence of high pressure in the tubular members can result in a leak at both the primary and secondary seal surfaces in this type of seal. Furthermore, this type of seal ring is relatively difficult to manufacture since it requires the formation of peripheral grooves and frustoconical surfaces of the seal ring and tight tolerances with respect to the length of the seal ring and the annular sealing recesses in the flanges.
There is described in U.S. Pat. No. 712,047 a bifrustoconical seal ring which is wedged into frustoconically tapered sealing recesses formed in the ends of hoses, pipes or fittings. This joint employs a seal ring and annular flange recesses which have flat ends which do not function as a seal. Instead, the seal is formed by severe wedging of the seal ring into the annular recesses of the opposed flanges, i.e. the seal ring relies on radial camming on the frustoconical surfaces into engagement by tightening the flange nuts to form a seal. Such a seal is generally adversely effected by the presence of any dirt on the sealing surfaces, and such adverse effects on the seal are not readily overcome by additional tightening of the seal. It is also stated at page 2, lines 9-10, of this patent that the seal surfaceiis preferably a little rough. In addition, this seal may be adversely affected by thermal expansion by temperature changes in the fluid flowing in the tubular member or pipe because of different rates of expansion between the seal ring and the flanges.
U.S. Pat. Nos. 4,214,779 and 1,150,249 may also be relevant background to the present invention.